1. Field of the Invention
The present invention relates to a novel multi-functional linear siloxane compound, a siloxane polymer prepared from the siloxane compound, and a process for forming a dielectric film by using the siloxane polymer. More particularly, the present invention relates to a novel multi-functional linear siloxane compound which can be changed into a polymer having advantageous mechanical properties, e.g., modulus, superior thermal stability, a low carbon content and a low hygroscopicity; a siloxane polymer prepared by the homopolymerization of the linear siloxane compound or the copolymerization of the linear siloxane compound with another monomer; and a process for forming a dielectric film which comprises the step of heat-curing a coating solution containing the siloxane polymer.
2. Description of the Related Art
In recent years, as the integration density of semiconductor integrated circuits has increased, the transmission of electric signals between wirings has slowed due to an increased RC delay. For this reason, there is a growing interest in lowering the capacitance of interlayer insulating thin films for semiconductor devices. For example, U.S. Pat. Nos. 3,615,272, 4,399,266, 4,756,977 and 4,999,397 disclose polysilsesquioxane dielectric films having a dielectric constant of about 2.5˜3.1 which can be formed by spin-on-deposition (SOD). The polysilsesquioxane dielectric films can replace conventional SiO2 dielectric films which have a dielectric constant of about 4.0), formed by chemical vapor deposition (CVD). On the other hand, hydrogen silsesquioxanes and a number of preparation processes thereof are well known in the art. For example, U.S. Pat. No. 3,615,272 teaches a process for preparing a completely condensed hydrogen silsesquioxane by condensing trichloro-, trimethoxy- or triacetoxysilane in a sulfuric acid medium. Further, U.S. Pat. No. 5,010,159 discloses a process for preparing a hydrogen silsesquioxane by hydrolyzing a hydridosilane in an arylsulfonic acid hydrate-containing hydrolysis medium to form a resin, and contacting the resin with a neutralizing agent. Further, U.S. Pat. No. 6,232,424 suggests a highly soluble silicone resin composition having excellent solution stability which is prepared by hydrolyzing and condensing a tetraalkoxysilane, an organosilane and an organotrialkoxysilane in the presence of water and a catalyst. U.S. Pat. No. 6,000,339 reports a process for preparing a silica-based compound which has improved oxygen plasma resistance and other physical properties, and enables the formation of a thick-layer. According to this process, the silica-based compound is prepared by reacting a monomer selected from alkoxysilanes, fluorine-containing alkoxysilanes and alkylalkoxysilanes with an alkoxide of titanium (Ti) or zirconium (Zr) in the presence of water and a catalyst. U.S. Pat. No. 5,853,808 discloses siloxane and silsesquioxane polymers useful for preparing SiO2-rich thin films wherein the polymers are prepared from organosilanes having a β-substituted reactive group, and the thin film compositions containing these polymers. Also, alkoxysilane compositions and insulating thin films formed by using these compositions are described in EP 0 997 497 A1. These compositions are obtained by hydrolyzing and condensing a mixture of at least one alkoxysilane selected from monoalkoxysilanes, dialkoxysilanes, trialkoxysilanes, tetraalkoxysilanes and trialkoxysilane dimers. In addition, U.S. Pat. No. 5,378,790 discloses organic/inorganic hybrid materials having excellent physical properties. Korean Patent No. 343938 discloses a siloxane composition prepared by hydrolyzing and condensing a cyclic siloxane monomer, and a dielectric thin film formed by using this composition.
However, dielectric thin films formed by using the siloxane polymers prepared from the prior art have the problem of an insufficiently low dielectric constant. Because they have a low dielectric constant, they possess poor mechanical properties. Additionally, they exhibit a limited applicability to semiconductor processes due to a high organic carbon content. In particular, in the case of a polymer prepared from a “Q”-shaped Si compound such as tetramethoxysilane, there is the problem of a high hygroscopicity, despite a low organic carbon content and good mechanical properties in the dielectric films, causing a drastic increase in the dielectric constant. Accordingly, the polymer has limited applicability to dielectric films, particularly those formed by the SOD process. In recent years, there has been an increased demand for combining siloxane polymers highly compatible with pore-forming materials so as to create a lower dielectric constant.
Thus, there is a need in the art to develop a material for forming a dielectric film by the SOD process which has a low dielectric constant, superior mechanical properties, e.g., modulus, excellent compatibility with pore-forming material, and markedly improved applicability to semiconductor processes, due to a low carbon content.